Directive antenna system



Oct. 17, 1950 w sBu 2,526,098

DIRECTIVE ANTENNA SYSTEM Filed; m. 11, 1949 In ventor John M. TewksburyPatented Oct. 17, 1950 UNITED STATES PATENT" orsicsy I 2,526,098. I I gs DIRECTIVE ANTENNA SYSTEM John MrTewksbury, Skowhegan, MaineApplication January 11, 1949, Serial No."70,284 5 Claims. (Cl. 250-3351)This invention relates to directive antenna systems and it hasparticular reference to an antenna obtaining directional effects withoutthe use of reflectors or auxiliary antennae.

In order to obtain directional effects it has been the practice eitherto use antenna wires which are specially shaped or to utilize standingwave energy produced by a reflector or an auxiliary antenna. All thesearrangements require a rather elaborate scheme to be followed whenmounting the antenna, as the dimensions of a number of parts, theirdistance etc., have to be adjusted to the wave length used.

The invention has. for its main object to provide an antenna producingdirectional effects which are inherent in the unit containing theradiating wire, so that merely the length of the unit has to be selectedin accordance with the wave lengthof the waves which are radiated. i

It is a-further object to provide a simple an .tenna system consistingmerely of ara'diating' member and a dielectric body surrounding thesame.

A further object of the invention consists in providing an antennasystem consisting of a radiating wire or tube fitted into a dielectricbody which may be either permanently held within said body or which maybe inserted into it to form the directive antenna system.

A further object of the invention consists in providing a dielectricbody surrounding the radiating antenna wire, producing a directionaleffect by a varying influence on the radiation in different directions,and adapted to produce a directed wave.

A still further object of the invention consists in providing theradiating antenna wire with a dielectric envelope or sheath adapted toinfluence the electromagnetic waves radiated withinan arcuate segment insuch a way that they are deflected with their direction a of propagationchanged by refraction so as to point in a given direction.

} selective or directional effect may be A further object of theinvention consists in antenna contained within and surrounded byadielectric body of substantially cylindrical shape having a biscuitshaped cross section, with a bridge or neck piece containing the antennawire joining the two enlarged portions of the dielectric body which arepositioned on two sides of the antenna wire in order to produce arefraction of the electromagnetic waves emanating from the radiatingantenna wire along an arcuate sector, propagation of the waves of saidsector being providing a radiating the direction of the changed so as toform a beam with a straight wave front. v g

The principle on which the invention is based consists in providing theradiating antenna wire or "tube with a dielectric body enveloping it andso shaped that the radiation penetrating'said body travels along pathsof different lengths, slowing down the velocity of propagation andtherefore producing a refraction of different extent in diiferentdirections. The shape. of the dielectricsubstance may be so" selectedthat the resulting wave front is a straight line wherebya produced. Theantenna consisting of the antenna wire or tube and the dielectric bodymay be manufactured as a single be manufactured separately, with achannel provided in it, into which the antenna wire or tube may beinserted.

.The joining of the two members in the last mentioned case is however asimple, mechanical operation not requiring skill or separate calculationor adjustment.

It will also be clear that the dielectric body with or without theantenna Wire embedded into it may bemanufactured in any length, forinstance, by extrusion from a nozzle, and may be cut off from a coil orthe like at the required length for use in specific cases.

Further more specific objects of the invention will be apparent from thefollowing specification.

The invention is described with reference to the accompanying drawing,illustrating an embodimentby way of example. It is to be understoodhowever that this example serves solely the purpose of explaining theprinciple of the invention 'and one mode of applying said principle. Itwill also be understood that'this principle has to be appliedindividually and that therefore modifications of the shape of thestructure and The principle of the invention is best illustrated withreference to Figure 1 which illustrates the unit, or the dielectric bodymay propagation of waves radiating outwardly from a center 0. Withradiation in air the radiation travels at a given time from O to A whichdistance is equal to that on any other ray OB, OC radiating from 0. Letit now be assumed that the ray OD has to travel through a dielectric inwhich the velocity of Wave propagation is much smaller than the velocityof propagation in air. In this case, while the rays OB and travel asbefore and reach points B and C after a given interval, the raytravelling along radius 0A only reaches point D on account of thereduced speed of wave propagation.

If it is further assumed that intermediate rays such as OE are retardedcorrespondingly by a dielectric offering less resistance than thedielectric along ray OD, it will be clear that in this way a straightwave front instead of a circular wave front will be obtained.

As refraction of the Waves occurs when they travel from a medium ofgreater density into a medium of less density, the rays OE are alsodeflected, the angle on of entry between the ray OE and the line Pperpendicular to the tangent at the point E being smaller than the angleat which the ray emerges. If the shape of the body of dielectricmaterial surrounding the center of radiation is properly chosen a beamin the direction OD, 0G is radiated, concentrating the rays emanatingbetween the rays OH, 01 in this direction.

The shape of the dielectric body 5 depends on the dielectric constant eon account of the relation 4 t for instance by extrusion in such amanner that the wire I is covered by the body 5, and may be hardened andcoiled, the length necessary for an antenna of the desired wave lengthbeing cut from the coil. It will be understood that the drawing is on alarge scale and that under most conditions the dielectric body is muchsmaller than shown.

In Figure 4 an antenna is shown consisting of a tubular body 9 such asused for short waves surrounded by the dielectric bodyki. The, tubularantenna may be removable and the dielectric body is manufacturedseparately in this case, with a cylindrical channel corresponding to thediameter of the tubular antenna. Both pieces are cut to the same lengthand the tube is then inserted into the channel.

of the electromagnetic Waves in air which'is practically equal to thevelocity of light, and e is the dielectric constant of the materialused.

Dielectric materials which are practically suitable for the purposeindicated are for instance the plastics; but also other materials, suchas glass, porcelain, etc. may be used, although their dielectricconstant is lower.

When a body of plastic is used, it may beproduced by extrusion, with theantenna wire 1 already embedded into it. A cross section through anantenna of this type is shown in Figure 3, 5 being ie dielectric bodysurrounding the antenna wire i which in this example is approximately inthe shape of a cylinder, the basis of which is a Boothian or Bernoullianlemniscate.

A special bridge piece or neck portion 8 may be provided in the middleportion of the body surrounding the antennawire i for the purpose ofincreasing the mechanical resistance of the structure and of joining thetwo sections or halves of the dielectric body, so that it may bemanufactured as a single piece surrounding the wire. On the outside saidbridge piece or neck portion may be lined with metal conductors.

The cross section producing the desired directional properties willhowever differ in shape with every material used and must therefore becalculated separately for each material.

The antenna thus produced, while diffusing some energy 'in the directionperpendicular to the main direction GOD, concentrates the radiationenergy emanating along the are 7 defined by the rays I01 and HOH in thedirection GOD.

The antenna as will be clear may be produced The invention thus providesa directional antenna of an extremely simple type, the direc tionalproperties of which are inherent in the antenna itself, so that nofurther structure such as an auxiliary antenna and no shaping or bendingof the antenna is necessary.

When such an antenna is used as a vertical antenna the direction ofpropagation of the waves is the planepassing through the antenna in thedirecti-on'GOD. When the antenna is used While in a horizontal position,the. plane GOD must be so positioned as to occupy the angle towards thehorizontal at which radiation is intended. If for instance, radiationat. a'certain angle is intended, in order to promote reception byreflection from the upper layers of the atmosphere at a given distance,the antenna or the dielectric r body surrot'inding.v the tube must beadjustedaccordingly. Likewise, if directional reception is intended, thedielectric body must be mounted and turned accordingly; I

It willalso beclearithat :the directive or selective propertiesofxthe'antenna arepracticaliy the same whether the antenna is usedfortransmiss-ion or forire'ception purposes.

'It will finally .be understood that the shape of the dielectric andother factors which are.vari= able may changeintthe manner required inaccordance with the above explained principle of the invention and thatchangescf other factors which are not essential, such as the, cross section of the antenna Wires may depart from those shown in the drawingwithout any departure from the essence of the invention.

Having described the invention, claimed as new is:

1. A directional antenna comprising a cylindrical body of plasticswithan antenna wire embedded in the axis of the body along the axis of thecylinder, thegeneratrices of the cylinder being parallel to the antennawire and the directrix of thelcylin'der being substantially a lemniscateWith the antenna Wire positioned at the inter? section of the branchesof the 'lemniscate. V

2.- A directional antenna comprising a radiate ing antenna wire,embedded, along its entire length in the center of a dielectric body,said dielectric body being a cylinder, the generatriccs of which .areparallel to;,the antenna wire, while the directrixrunsaiong a curvedsubstantially closed path on each side of the antenna wire, so as toform two substantially closed cylindrical sections, located on the twosides of the antenna Wire, and a cylindrical neck portion between saidtwo substantially closed cylindrical sections, surrounding saidantenna-wire.

3. A directional antenna as claimed in claim 1 in which the cylindricaldielectric body is prowhat is the periphery vided with a central channeland in which the antenna wire is formed by a tubular conductor fillingthe said central channel.

4. A directional antenna comprising a conducting and radiating antennawire, and a dielectric body arranged in two substantially cylindricalsections on two diametrically opposite sides of said antenna wire,symmetrically with respect to a median plane including the antenna wireand at right angles to the direction of wave propagation, thegeneratrices of the cylindrical surfaces of the aforesaid sections beingparallel to the axis of the antenna wire and the cross section of eachcylindrical section at right angles to the last named plane of symmetryincreasing in width with its distance from the antenna wire to a maximumand then decreasing,

of each cross section of a, cylindrical section being thus so shapedthat the vector drawn from the center of radiation towards points of theperiphery of the cross section of a cylindrical section increases withthe increase of the vectorial angle between said vector and said medianplane.

5. A directional antenna comprising a dielectric body and a conductingand radiating an tenna wire embedded therein, said dielectric bodyconsisting of two substantially cylindrical sections arrangedsymmetrically on both sides of 6 the antenna wire with the generatricesof the cylinders arranged in substantial parallelism to the antennawire, each section having a substantially closed curve as a directrix sothat its cross section increases to a maximum and then decreases withthe distance from the axis of the antenna wire, so that lines drawn fromthe central axis of the antenna wire toward points of said curvedsurface of the cylindrical section increase in length with decreasingangle totwo cylindrical sections and including the antenna wire, saidincrease of length being such that a straight wave form in the maindirection of wave propagation is produced.

JOHN M. IEWKSBURY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

